1. Field of the Invention
The present invention generally relates to a charge pump circuit, and more particularly, to a charge pump circuit having comparatively fewer capacitor components.
2. Description of Related Art
Typically, in an electronic circuit, voltages of different levels are often needed for operation of the circuit. Therefore, a charge pump is often employed in such an electronic circuit for generating voltages of different level.
FIG. 1 is a circuit diagram of a conventional charge pump. Referring to FIG. 1, there is shown a charge pump circuit 100 including switches 101 through 108, capacitors 109 through 112. The charge pump circuit 100 utilizes two control signals PH1 (in first periods) and PH2 (in second periods) for alternately controlling on/off states of the switches 101 through 108. When the control signal PH1 is at a high level, the switches 101, 104, 106 and 108 are turned on, in which an equivalent circuit is as shown in FIG. 2A. In this case, an input voltage VIN charges the capacitor 109 to hold a voltage difference at two terminals thereof that equals to VIN. When the control signal PH2 is at a high level, the switches 102, 103, 105, and 107 are turned on, in which an equivalent circuit is as shown in FIG. 2B. In this case, the input voltage VIN and charges stored in the capacitor 109 charge the capacitors 110 and 111 to 2VIN, and generate an output voltage Vout1 with a level of 2VIN.
Then, when the control signal PH1 is again shifted to the high level, in which the capacitor 110 stores charges of 2VIN, the output voltage Vou1 is sustained as 2VIN. Meanwhile, the capacitor 112 is charged by charges stored in the capacitor 111, so as to generate another output voltage Vout2 with a level of −2VIN.
FIG. 3 is a circuit diagram of another conventional charge pump. Referring to FIG. 3, there is shown a charge pump circuit 300 including switches 301 through 306, capacitors 307 through 309. The charge pump circuit 300 utilizes four control signals PH1 (in first periods) through PH4 (in fourth periods) for alternately controlling on/off states of the switches 301 through 306. When the control signal PH1 is at a high level, the switches 301 and 304 are turned on, in which the charge pump circuit 300 has an equivalent circuit as shown in FIG. 4A. In this case, an input voltage VIN charges the capacitor 307 to hold a voltage difference between two terminals thereof identical to VIN. When the control signal PH2 is at the high level, the switches 302, and 303 are turned on, in which the charge pump circuit 300 has an equivalent circuit as shown in FIG. 4B. The capacitor 307 has a terminal coupled to the input voltage VIN. The capacitor 308 is charged to 2VIN by the input voltage VIN and charges stored in the capacitor 307, and thus outputting an output voltage Vout1 with a voltage level of 2VIN.
When the control signal PH3 is at a high level, the switches 301 and 304 are turned on, in which the charge pump circuit 300 has an equivalent circuit as shown in FIG. 4C. In this case, the capacitor 308 stores charges of 2VIN, and therefore the output voltage Vout1 sustains a voltage level of 2VIN. On the other hand, the input voltage VIN charges the capacitor 307 to hold a voltage difference between two terminals thereof that equals to VIN. When the control signal PH4 is at the high level, the switches 305 and 306 are turned on, in which the charge pump circuit 300 has an equivalent circuit as shown in FIG. 4D. In this case, the capacitor 309 is discharged by the charges stored in the capacitor 307, so as to generate another output voltage Vout2 with a voltage level of −VIN.
Generally, with respect to a charge pump circuit, built-in capacitors occupy a large area of the integrated circuit (IC), and thus the production cost is increased. On the other hand, external capacitors also occupy additional areas on the circuit board, and thereby increase the production cost, and even make the product bulky. Further, although the conventional charge pump circuit 100 is capable of outputting output voltages 2VIN and −2VIN. The output voltages Vout1, Vout2 both require a stabilization capacitor, which increases the production cost. Furthermore, although the conventional charge pump circuit 300 uses capacitors one less than the charge pump circuit 100, it produces a negative voltage of only −VIN. The conventional charge pump circuit 300 employs four control signals (correspondingly in four periods) for generating output voltages of 2VIN and −VIN, and therefore has a lower efficiency, and a lower maximum load capability.